Direct Injection Gasoline (DIG) fuel injection in an internal combustion engine involves injection of fuel directly into each combustion chamber. A high range of fuel flows is required to meet engine power demands ranging from very low idle speed to peak power.
It is known in the art that a variation in net hold force (force required of an injector solenoid to hold the valve open against closing spring force and fuel pressure) at a specific applied current is responsible for a large portion of the variation among fuel injectors in closing response and therefore in flow and linear range variation. The variation in hold force is associated with several dimensions, and also with batch-to-batch magnetic characteristic variation in materials of construction, and also with mechanical tolerances caused by machining of individual components.
It is known in the diesel engine arts to determine flow characteristics of each fuel injector at a fixed hold current and to program this information into the Engine Control Module (ECM) at the time of engine assembly, allowing the ECM to compensate at least partially for variations in flow differences among the injectors in an engine by varying instructions to the individual injectors.
This approach, however, does not address the more fundamental problem of variation in performance with variations in mechanical and magnetic properties and does not provide sufficient correction for a DIG engine. Further, it is desirable that a specified hold current (expressed by the ECM as an applied voltage) be great enough to assure that the injector valve stays fully open for the desired period but not so great as to delay closing of the valve due to extended hysteresis in collapse of a larger-than-necessary magnetic field.
This problem is addressed by at least two US patents.
U.S. Pat. No. 5,241,858 is directed to a dynamic flow calibration of a fuel injector by selective diversion of magnetic flux from the working gap. The fuel injector has a dynamic flow calibration mechanism in which a control rod that extends between and enters holes in both the stator and the armature is selectively positioned to divert some of the magnetic flux from the axial working gap between the stator and the armature such that the diverted magnetic flux passes through the control rod directly between the stator and the armature without passing through the working gap. The fuel injector is calibrated by selectively positioning the control rod so that the diverted flux which is conducted between the stator and the armature is conducted through the control rod without passing through the working gap.
U.S. Pat. No. 5,392,995 similarly is directed to a fuel injector calibration through directed leakage flux. The solenoid includes a tubular pole piece with an area of increased reluctance adjacent the working surface of the pole piece and an adjustment rod disposed for movement within the high reluctance region to thereby vary the location at which the high reluctance region begins. Leakage flux from the high reluctance region of the magnetic circuit may be directed to operate on a particular element of the magnetic circuit based on the location of the adjustment rod thereby allowing the leakage flux to exert a force on the element and to thereby vary the dynamic response characteristics of the injector.
Neither of these inventions addresses the problem of an injector having a specified and fixed hold current that is inadequate for reliably keeping the injector valve fully open for the desired length of time under all operating conditions.
Further, both of these inventions require very substantial modifications to a standard fuel injector, including an expensive and cumbersome moveable rod and rod-positioning mechanism.
What is needed in the art is a method for providing to an ECM a characterization of the electrical and mechanical properties of each fuel injector in an internal combustion engine, such that the ECM can vary, via an algorithm, one or more electrical parameters for each injector to equalize the fuel injection characteristics of all the injectors in the engine. The method should be readily applicable to standard prior art fuel injectors and not require special modifications to the fuel injectors.
It is a principal object of the present invention to equalize the fuel flows among a plurality of standard fuel injectors in an internal combustion engine.